Title

Author

Date of Award

1997

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine and Atmospheric Chemistry

First Committee Member

Eric S. Saltzman, Committee Chair

Abstract

The biogeochemical cycling of methyl bromide in the oceans is investigated through the determination of production and removal rates. Since atmospheric methyl bromide has been determined to contribute to the destruction of stratospheric ozone, phase-out of the production of methyl bromide has been proposed (Montreal Protocol and U.S. Clean Air Act). However, the large uncertainty associated with the budget and lifetime of atmospheric methyl bromide makes it difficult to predict the effect of this policy. The cycling of methyl bromide in the oceans is a large component of this uncertainty since the oceans are both a source and a sink of atmospheric methyl bromide, on a regional basis. An investigation into the production and removal rates of methyl bromide in the ocean would improve the current understanding of the role of the oceans in the lifetime of methyl bromide in the atmosphere.Production of methyl bromide is observed in cultures of one cold water and two warm water species of phytoplankton. Extrapolations of the measured production rates cannot account for the observed oceanic methyl bromide concentrations. This implies that more work is necessary to determine the primary biological source of methyl bromide to the oceans.An isotope dilution gas chromatography-mass spectrometric technique was developed for high precision measurement of methyl bromide in seawater samples. This technique was used for the measurement of the removal rate of methyl bromide in incubated seawater samples. Measurements of the chemical removal rate constant in seawater agree with previously published values and help to decrease the uncertainty associated with the temperature dependence of that process.Measurements of the removal rate constant of methyl bromide in unfiltered, coastal subtropical seawater samples indicate that biological removal does occur and at rates which are significant at environmental levels. Initial filtration experiments imply that the removal is the result of bacterial activity, although further experiments are required to confirm this theory. The relative importance of biological removal, as compared to chemical removal, of methyl bromide could be more significant in high latitude regions where biological activity is high but chemical removal is slow.